Abstract

The shadowing and blocking effects exhibited by medium energy ion scattering (MEIS) make it a uniquely effective technique for the analysis of the layer composition of bimetallic surfaces. We use MEIS to study adsorbate-induced segregation effects at the Cu50Pd50(110) surface. We show that the clean surface composition is strongly dependent on sample preparation. In addition, the adsorption of chlorohydrocarbons causes substantial surface layer Cu enrichment (up to 100% Cu), whereas hydrocarbon adsorption causes Pd enrichment. We propose an explanation for the magnitude of these segregation effects in terms of the surface chemistry of these molecules